1. Field of the Invention
The present invention relates to a display panel driving method, a display panel driver circuit, and a liquid crystal display device, which are capable of inverting a polarity of a data signal which is applied to respective picture elements of a display panel every predetermined time, i.e., executing the alternating current drive and, more particularly, an active matrix type liquid crystal display panel driving method, a liquid crystal panel driver circuit, and a liquid crystal display device.
2. Description of the Related Art
In recent years, as a display for OA devices such as the notebook computer (mobile PC), etc. as well as various devices such as the digital video camera, the telephone, etc., the liquid crystal display device is rapidly spreading. Such liquid crystal display device is still inferior in screen size, picture quality, cost, etc. to the displaying means such as the CRT (cathode ray tube), etc., nevertheless its excellent features such as low power consumption, light weight, space saving, etc. are watched with interest.
The active matrix type liquid crystal display panel has such a structure that a liquid crystal is sealed between two glass substrates. A plurality of picture element electrodes, which are arranged in the horizontal direction and the vertical direction, and a plurality of switching elements, which turn ON/OFF the voltage applied to the picture element electrodes, are formed on one glass substrate. As the switching element, a thin film transistor (abbreviated as a “TFT” hereinafter) is often employed.
Also, color filters and opposing electrode are formed on the other glass substrate. These two glass substrates are arranged such that a face on which the picture element electrodes are formed and a face on which the opposing electrode are formed are opposed to each other. Three color filters, i.e., red (R), green (G), blue (B) filters are formed as the color filters. The R, G, B color filters are arranged in predetermined sequence to correspond to respective picture element electrodes. The substrate having the TFTs thereon is called a TFT substrate, and the substrate having the opposing electrode thereon is called an opposing substrate.
In addition, a pair of polarizing plates are arranged so as to put the TFT substrate and the opposing substrate, between which the liquid crystal is sealed, between them. Normally, polarizing axes of a pair of polarizing plates are arranged to intersect orthogonally with each other.
FIG.1 is a block diagram showing an example of a liquid crystal display device in the prior art. As shown in FIG.1, the liquid crystal display device comprises a liquid crystal display panel 501, a data driver include a plurality of data driver IC 502, a gate driver include a plurality of gate driver IC 503, an input controlling portion 505, and a reference voltage power supply 506.
A plurality of picture elements (not shown) which are arranged in a matrix, a plurality of data bus lines 502a and a plurality of gate bus lines 503a, and a plurality of TFTs (not shown) which are connected between the picture elements and the data bus lines 502a and the gate bus lines 503a respectively are provided to the liquid crystal display panel 501. The data driver 502 outputs data signals (display data) to the data bus lines 502a. The gate driver 503 outputs a predetermined scanning signal to the gate bus lines 503b in sequence at timings which are in synchronism with the horizontal synchronizing signal. The TFTs are turned ON when the predetermined scanning signal is supplied to the gate bus lines 503a to transmit the data signals, which are supplied to the data bus lines 502a, to picture element electrodes.
The input controlling portion 505 receives signals such as image signals, synchronizing signals, operating clocks, etc. from a display control information source (referred to as a “personal computer” hereinafter) 504 such as a personal computer, and then outputs the image signals to the data driver 502 at predetermined timings and also supplies the clock signals to the gate driver 503. The reference voltage power supply 506 supplies reference voltages, which is applied to the picture elements, to the data driver 502.
FIG. 2 is a block diagram showing a configuration of the input controlling portion 505 of the liquid crystal display device in the prior art.
The input controlling portion 505 is composed of an input interface (I/F) portion 511, an input data latch circuit 512, and a data output circuit 513. The input. I/F portion 511 receives display control information (the image signal, the horizontal, and vertical synchronizing signal, the operation control signal, etc.) from the personal computer 504, and transmits predetermined signals to the input data latch circuit 512, the data output circuit 513, etc. The input data latch circuit 512 holds temporarily the image signals (R, G, B). Also, the data output circuit 513 performs timing control, waveform shaping, etc. of the image signal, and then outputs them to the data driver 502.
In such configuration, the image data which are received via the input I/F portion 511 are output to the data driver 502 at a predetermined timing via the input data latch circuit 512 and the data output circuit 513. Based on an inverting period of the reference voltage supplied from the reference voltage power supply 506, the data driver 502 inverts the polarity of the data signal, which is applied to the picture element, at a predetermined period.
Where the wording “inverting period of the reference voltage” means such an inverting period that the reference voltage being applied between the picture element electrode and the opposing electrode in the liquid crystal display panel repeats a positive polarity voltage and a negative polarity voltage invertedly relative to a common voltage alternatively. Normally, such inverting period of the reference voltage is set to a constant inverting period.
As described above, the active matrix type liquid crystal display panel can be driven by the alternating current voltage. For example, the voltage whose polarity can be changed into a positive polarity (+) and a negative polarity (−) every predetermined time interval with respect to the voltage, which applied to the opposing electrode, is supplied to the picture element electrode. It is preferable that the voltage being applied to the liquid crystal should have a positive voltage waveform and a negative voltage waveform symmetrically. However, even if the alternating current voltage which has the positive voltage waveform and the negative voltage waveform symmetrically is applied to the picture element electrodes, the positive voltage waveform and the negative voltage waveform which are applied actually to the liquid crystal are not formed in a symmetrical manner. Therefore, a transmittance of light obtained when the positive voltage is applied and a transmittance of light obtained when the negative voltage is applied become different. As a result, a luminance is varied in a period of the alternating current voltage being applied to the picture element electrode to thus cause a flicker. This phenomenon is called a flicker.
In the prior art, a method of changing the voltage applied to the opposing electrode, a method of setting the polarity of the voltage applied to the adjacent picture element electrodes differently in the horizontal direction and the vertical direction, and a method of increasing the frequency of the polarity inversion are known as a method of suppressing such flicker. For example, such technologies have been disclosed in Patent Application Publication (KOKAI) Sho 62-113129, Patent Application Publication (KOKAI) Hei 2-34818, Patent Application Publication (KOKAI) Hei 6-149174, Patent Application Publication (KOKAI) Hei 7-175448, and Patent Application Publication (KOKAI) Hei 9-204159.
In case the voltages which has the different polarity are applied to the adjacent picture element electrodes, there may be considered (i) a method by which the voltage with the same polarity is applied to the picture element electrodes being aligned in the vertical direction while the voltage with the opposite polarity is applied to the neighboring picture element electrodes being aligned in the horizontal direction, (ii) a method by which the voltage with the same polarity is applied to the picture element electrodes being aligned in the horizontal direction while the voltage with the opposite polarity is applied to the neighboring picture element electrodes being aligned in the vertical direction, (iii) a method by which the voltages with mutually different polarities are applied to the picture element electrodes being adjacent in the vertical direction and the horizontal direction, etc. Where the pattern indicating the polarity of the voltage, which is applied to the picture element electrodes of the liquid crystal display panel, is called the polarity pattern.
The inventors of the present invention have concluded that the above prior art contains following problems. That is, the flicker becomes conspicuous when the vertical-striped pattern (display pattern) is displayed in the polarity pattern (i), when the lateral-striped pattern is displayed in the polarity pattern (ii), and when the mosaic pattern (checker pattern) is displayed in the polarity pattern (iii). These patterns (display patterns) are relatively often used in the display for the computer system.
Also, according to the method of changing the voltage applied to the opposing electrode, the control becomes complicated and also the circuit scale is increased. In addition, according to the method of increasing the inverting frequency, the circuit configuration becomes complicated.